[ovirt-users] About the vm memory limit

I would like to ask if there is any limit on the memory size of virtual machines, or performance curve or something like that? As long as there is memory on the physical machine, the more virtual machines the better? In our usage scenario, there are many virtual machines with databases, and their memory varies greatly. For some virtual machines, 4G memory is enough, while for some virtual machines, 64GB memory is needed. I want to know what is the best use of memory for a virtual machine, since the virtual machine is just a QEMU emulation process on a physical machine, and I worry that it is not using as much memory as a physical machine. Understand this so that we can develop guidelines for optimal memory usage scenarios for virtual machines. Thank you!